I have a 406 cu. in. small block chevy in my Malibu.
The motor was built with a 350 crank so I believe it is now an internally balanced motor?
The harmonic balancer is smooth on both sides with no weight or different size cut outs on it.

I have an aluminum Flywheel that was for the 400 cu. in. Externally balanced engine.

My question is, Can I remove the counter weight that is bolted on the back side of this flywheel with 2 bolts and use it on my internally balanced small block engines?

you may be able too, but the issue of how the flywheel is balanced does differ between manufactures, (no I don,t have a list) on some the weights can be removed to get neutral balance, on some the external weights NOT the only difference in the flywheel balance
personally ID call the flywheel manufacture and ask... and yeah! you might need to have the assembly balance and use the flywheel. but a good machine shop that does engine balancing should be easily able to test and get that flywheel to meet the factory balance specs.
obviously it would help if you know or have the balance sheet and know the bob-weights the 350 crank,rods,pistons,rings, bearing and piston pins have, that were used

(thats a good point) and he should have made that clearer,
I was assuming he meant the engine he has was a 350 crank, being used with main bearing spacers in a 400 block (377) (a common engine build for performance)

The 406 cu. in. in my Malibu was built by a shop near my house.
I am not sure if he used the crank spacers or not, but I do know now that it is "Internally" balanced.
It is a 400 block and was bored .030 over.
I ordered a new Aluminum 11" flywheel for it (American Powertrain Part# FWCV-20002) from Summit for a (400 cu. in. Externally Balanced engine)to replace the old, cast Iron one not realizing that the 400 he built for me was internally balanced.
After the swap, it vibrated like crazy!
I took the trany back out and then realized it was a "Bolt-on" counter weight.
The new clutch that I ordered with it was a Center Force "Dual-Friction" DF148552 Part #183-DF148552.
Maybe I should have bought a Center Force Aluminum Flywheel($650.00)to match the Center force dual friction clutch but now that I have this one, they want $120.00 re-stocking fee (and that is only if it shows no signs of wear and not used) It was bolted to the engine and started in my garage so I know there are some bolt marks on it.
I am hoping that I can just remove this counter weight and have a Neutral balance flywheel and use it on this 406. cu. in. internally balanced engine. This motor put out 510 HP. on his engine dyno.
Is there a specific amount of weight added to all manufactures flywheels that are used to balanced the 400 cu. in. chevy mouse motors? or does this vary from motor to motor or flywheel manufacture to manufacturer?
If I know this, I can weigh the counter weight and screws that I just removed from this flywheel to see if it adds up?

All flywheel weights for a factory 400 crank should be the same. If your weight is a separate piece, just put the flywheel back on without it and bolt everything together.

To avoid this problem when you buy parts in the future, just tell the vendor you have a 377 engine (which you do) and NOT a 406. Whoever told you that you have a 406 should not be allowed anywhere near your car with tools.

Ray

There's a line between good and evil no wider than a razor's edge - D.S. James Hathaway quoting from The Night Keeper

This is a 400 Block bored .030 over with a stroked 350 crank.
It is a 406 cu. in. but internally balanced motor.
All is good now that I have removed the counter weight off the flywheel.
Ye! Hawaaa!
Thanks for everyones input!

Possibly, but I can't see why anyone would want to stroke a 350 crank if it were to be used in a 400 block. The stroke would need to be about 3.74, which is almost the same as a stock 400 crank, and if you use a 400 crank instead, you won't need to deal with the main bearings. To put it another way, if you bore a 400 block .030, you get a 406 with the stock crank.

Ray

There's a line between good and evil no wider than a razor's edge - D.S. James Hathaway quoting from The Night Keeper